Magnetic device



April 26, 1960 FREUNDT 2,934,619

MAGNETIC DEVICE Filed May 12, 1958 INVEN 1 OR.

.netic structure.

Unite States Patent C MAGNETIC DEVICE Edmund John Freundt, Indianapolis, Ind., assignor to Gladys E. Freundt Application May 12, 1958, Serial No. 738,592

6 Claims. (Cl. 200--87) mum investment in equipment. The 60-cycle alternating current generally available is not basically suited to provide the low striking frequency of from 10 to 20 blows per second which is necessary in loud-ringing bells. Such devices as magnetic polarization, used in conjunction with a half-wave rectifier, and the use of geared gong-knockers, are examples of attempts to improve the basic vibrating bell to adapt it for use in loud-ringing applications. Previously available designs which have been developed for increasing the magnetic build-up of a device which operates its own control contacts, involve complexities in design or precision in manufacture which places severe limits on the use of such devices, due to their high cost of necessary maintenance. The present invention contributes to the basic technology of this art with a control device that is simple, durable, and easily manufactured at low cost.

The usual device which actuates its own control contacts, such as a bell or vibrating relay, is inherently a momentary contact type of device, capable of developing only a fraction of the power available in its electro-mag- Devices of this type produce high frequency, low-power vibrations of the armature, limiting the auditory utilization of the device to small bells, buzzers, or high frequency hummers. Low frequency, high power oscillations may be obtained only through the use of some control device to insure satisfactory build-up of the electromagnetic system.

Such a device should provide that the associated armature will traverse the desired distance before separating the contacts. The device should also provide that when its actuating coil is energized, and the normal resilient forces contained in the armature system, which normally act to close the movable contact, are as a consequence prevented from acting on the movable contact, the inherent friction of the movable contact system will maintain satisfactory contact pressure against the resilient force .of the fixed contact; which force, in conjunction with mechanical vibrations established by the entire device,

acts to separate the contacts, or to produce a condition of high electrical resistance between the contacts. Furthermore, when the armature displaces the movable contact to the open position, this position should be maintained with fidelity by the inherent friction of the control system, until the deenergized solenoid permits the armature to act under resilient forces to restore the system to the initial position. In addition, practical considerations limit the power of devices of this type to a usual value of about ten watts; and the maximum power available on the solenoid-actuated type is thus normally of the order of seven ounces. It is obvious that such a system can tolerate only a small amount of friction, and that the magnitude of this friction is directly associated with the restricted energy available on the resilientlypowered return stroke. Thus the friction of the control system should not only have a low value, but one which is very stable in its reflection to the armature system. It is also important to perceive that the armature, while opening the control contact during the power stroke, must close the control contact through the expenditure of its resiliently-stored energy; and this contact-closing must be accomplished at a point in the return stroke of the armature Where the resiliently-stored energy is almost dissipated. Hence, since said aramature offers a relatively long stroke during which the much shorter separation between the movable contact and the fixed contact is achieved, a suitable lever arm arrangement is necessary to transform the relatively high friction of the movable contact system, acting through a small arc of travel, to the lower value which the armature may easily tolerate through its much greater travel distance.

In accordance with the present invention, the objectives previously described are achieved through the use of a timing system which makes use of what may be generally described as the restraining force of a stable, magnetic brake system. This magnetic brake is associated with the operating arm that produces separation between the contacts, said operating arm being actuated by appropriate contact-actuating devices attached to the armature of the actuating device. In one preferred embodiment of the invention, a polytetrafluoroethylene washer is interposed between the fixed and movable portions of the magnetic brake, thereby maintaining a controlled air gap and controlling the friction between such members. In certain preferred embodiments of the invention, adjustable means are provided, comprising an adjustable contact-opener and an adjustable contact-closer, both being mounted on the armature, with the operating arm positioned in the adjustable space between said contact-opener and said contact-closer, so that during only a portion of the movement of the armature in one or both directions is the armature movement transmitted to the operating arm that separates the contacts. By this adjustment arrangement, a variety of stroke-time conditions may be obtained from one device, thus making it useful not only for bellringing, but for a variety of other uses.

A more detailed description of certain embodiments of the invention would include a system comprising a fixed, resilient contact; a movable contact, associated with a magnetic brake influenced by a permanent magnet and its friction control member; a source of electromagnetic energy, energized during the closing of said contacts; an armature movable electromagnetically by said source of electromagnetic energy; adjustable contact operators attached to the armature to open and close the electrical contacts, so that during only an adjustably controllable portion of the movement of the armature is the movement transmitted to the movable contact system; the armature and magnetic brake system all being influenced by yielding forces, being urged in a direction opposite from the direction urged electromagnetically.

In the accompanying drawing, the essential features of the invention are indicated, as applied to a solenoid operated device suitable for actuating a loud-ringing bell, or for actuating other contacts for control of the timing of other devices, or for similar types of applications. However, the invention is not limited to solenoid operated applications, since the conventional electromagnet with its efficient magnetic structure may equally well be utilized,

Referring now in detail to the preferred embodiment of the invention shown in the accompanying drawing in which brake plate 3 and friction control washer 11 are shown in a cut-away view to clearly indicate their relationship, a permanent magnet 1 is mounted so that magnetically susceptible brake plate 3 rests on the magnetic surface of the main pole faces of permanent magnet 1, with friction control washer 11 interposed between the pole faces of permanent magnet i and the hidden face of brake plate 3. Brake plate 3 is held against friction control washer 11 by the tractive effort of permanent magnet 1, said magnet producing a stable force normal to the face of brake plate 3. Permanent magnet 1 and friction control washer 11 are fixed to the base, but brake plate 3 is free to move over the surface of friction control washer 11 when urged by the movement of operating arm 2. In addition to the frictional restraining forces established by this system between brake plate 3 and friction control washer 11, any movement of brake plate 3 is. resisted by reactions associated with the movement of a conducting loop passing through a stationary magnetic field of high intensity. Brake plate 3 represents a complex, closed conductor; and in certain preferred embodiments of this invention, brake plate 3 has attached to one surface a suitable loop of high conductivity copper to facilitate the flow of eddy currents. Brake plate 3 is pivoted on pivot 4 to permit arcuate movement. To brake plate 3 is attached operating arm 2, and to operating arm 2 is attached movable contact 5. Movable contact 5 makes contact with fixed, but resilient contact 6 at such times as are proper in the operation of the device. Armature 8 has attached to it adjustable contact opener 9 and adjustable contact closer it]. Armature 23 receives electromagnetic energy from solenoid coil 7 when movable contact 5 and fixed contact 6 are not separated, and electrical energy is available at terminals 12 and 13. The required electrical energy may be AC. or DC. All parts are attached to a suitable base 14.

As is customary in devices which electromagnetically actuate their own contacts, operating arm 2 may be shifted from the contact closed position to the contact open position when solenoid coil 7 is energized, so that armature 8, influenced by magnetic forces, moves to the point where operating arm 2 is displaced by the movement of contact opener 9. At the instant that armature 3 begins its travel into energized solenoid coil 7, the magnetic brake system is released from the influence of armature 8. The contact system is now placed under the influence of the resilient force of fixed contact 6, which, in the absence of a suitable brake system associated with operating arm 2, would dissipate the resilient energy of fixed contact 6 by displacement of operating arm 2, resulting in loss of contact pressure between movable contact 5 and fixed contact 6, thus rendering the device inoperative. However, since operating arm 2 is influenced by an adequate brake system, the resilient energy of fixed contact 6 is balanced by the restraining action of the brake system; which, in addition, provides restraint against movement of operating arm 2 by reason of the appreciable vibrations established throughout the device by the rapid acceleration and deceleration of armature 8. Hence, normal contact pressure is maintained by action of the magnetic brake system during the time required for contact opener 9 to travel the distance required to displace operating arm 2 sufficiently to separate contacts 5 and 6. This time interval is controllable, and in consequence, solenoid coil 7 may be permitted to develop any fraction, or all of its possible magnetic strength; or additional time delay introduced, depending on the distance between contact opener 9 and contact closer it). After this time interval, solenoid coil 7 loses its energy, and armature 8 delivers its stored mechanical energy in the form of a blow upon a gong, or in some other desired manner. Then, under the influence of yielding forces, armature 8 begins its return stroke, which ends when operating arm 2 has been 4 displaced to the contact closed position, requiring the transfer of energy to the resilient system of fixed contact 6, in addition to the energy necessary to overcome the friction of the magnetic brake system.

One object of the magnetic brake system is to provide a stable force normal to brake plate 3, and to accomplish this without the use of springs, cams, detents or other mechanical devices; which same are either not practical because of hi h cost, or else are inexpensive but unreliable. This object I achieve by using the tractive force of a permanent magnet in a novel manner, so that it acts on a movable brake plate, which provides the equivalent of completely closed magnetic circuit. Under such conditions, high-grade, permanent magnets will retain their strength indefinitely. Thus I make use of an inexpensive source of almost constant force to maintain frictional reactions in a brake system. The combination of this stable force and the stable characteristics of the polytetrafiuoroethylene friction control washer produces a simple and reliable means of providing that operating arm 2 will resist displacement with a force which will remain indefinitely Within predetermined values, insuring practical utilization of the associated device; and furthermore, when operating arm 2 is displaced, it will maintain its new position with fidelity until displaced by the appearance of the proper force in the cycling of the system.

It is important to note that when armature 8 displaces contact closer it the yielding forces powering the armature return stroke are on the threshold of minimum value; and this occurs at a time when the energy demand is critical, in that the energy must be sufiicicnt to restore the brake and contact system to the point where normal contact pressure is again maintained between contacts. For this reason, a basic improvement is incorporated in this invention to make efficient utilization of the energy available to close the contacts. The basic improvement includes the novel use of a lever arm to compound the effect of resiliently powered armature forces, acting through their relatively large distance, with a small force applied, to overcome the effect of large frictional forces, acting through their relatively short distance. Thus, there is an operating arm distance between the center lines of armature 8 and pivot 4, with respect to the distance between the center line of pivot 4 and the centerline of the forces established by permanent magnet i, which utilizes with maximum efhciency the resiliently powered energy of armature S. This improvement materially betters the performance of the device by reducing the required resiliency of the device, thus leaving more useful energy for audible utilization, and at the same time adds to the reliability of the contact closing system.

Particular attention is directed to the action of the polytetrafiuoroethylene washer interposed between permanent magnet 1 and brake plate 3. This thin washer has a life far beyond the average life of contacts on devices of this type. The washer is valuable in control-ling the frictional relationship between permanent magnet -1 and brake plate 3, in that it provides a material having a known and stable coefiicient of friction between two metallic surfaces that otherwise might require periodic maintenance for control of their frictional characteristics. The thin material of this Washer does not materially impair the strength of the magnetic field between permanent magnet i and brake plate 3, and produces a very stable frictional arrangement without recourse to elaborate manufacturing processes or excessive cost.

The invention claimed is:

1. In a system comprising a movable electrical contact and a fixed electrical contact, a solenoid energized during the closing of such contacts, an armature movable electromagnetically by said solenoid, means actuated by the displacement of the armature to open and close the contacts, the armature and movable contact being yield- U ingly urged in a direction opposite from the direction urged electromagnetically, and means adapted to decrease the frequency of vibration of the armature and to increase the striking power of the armature, the improvement which includes the combination of: a brake plate attached to an operating arm, said brake plate being of magnetically susceptible metal, and capable of arcuate movement about a pivot, said pivot axial center line distance at right angles from the center line of the armature being the distance necessary to obtain normal separation between the fixed and movable contacts when the armature position is such that the contacts should be separated, a magnet associated with the brake plate to produce a magnetic brake with a friction controlling member interposed between the face of the active pole faces and the face of the brake plate, the operating arm having attached to it a contact which in conjunction with a fixed contact opens and closes the solenoid circuit, the operating arm being associated with the armature and displaceable by it through adjustable means, so that only during an adjustably controlled portion of the movement of the armature is the armature movement transmitted to the operating arm.

2. The system of,claim 1, in which the solenoid has metallic cores and acts as an electromagnet.

3. The system of claim 1, in which the brake plate is directly connected to the armature through a loose, adjustable connection, so that only during an adjustably controllable portion of the movement of the armature is the movement transmitted to the brake plate.

4. The system of claim 3, in which the solenoid has metallic cores and acts as an electromagnet.

5. A magnetic braking system containing the necessary elements described in claim 1, said elements being so arranged that the desired braking action is achieved through relative movement between the magnet and the brake plate.

6. Ina system involving an armature adapted to vibrate electromagnetically through its control over the contacts actuating its electromagnet, the combination of: a fixed electrical contact, a movable electrical contact, an electromagnet energized only during the closing of such contacts, means actuated by the displacement of the armature to open and close the contacts, the armature and movable contact being yieldingly urged in a direction opposite from the direction urged electromagnetically, and a brake which holds one contact in the most favorable position, when so required, to permit the desired timing of the magnetic build-up of the electromagnet.

References Citedin the file of this patent UNITED STATES PATENTS 692,579 Wotton Feb. 4, 1902 913,437 Schoeller et al. Feb. 23, 1909 1,174,230 Coleman Mar. 7, 1916 1,754,154 Fitzgerald Apr. 8, 1930 1,901,443 Garvin Mar. 14, 1933 2,488,443 Sonneman Nov. 5, 1949 2,610,995 Orsatti et a1 Sept. 16, 1952 

